1. Field of the Invention
The present invention relates to an organic peroxide having a polymerization-regulating ability, and more particularly relates to a peroxy aryl carbonate having a polymerization-regulating ability in the radical polymerization or copolymerization reaction of unsaturated monomers and further having a polymerization-initiating ability for the reaction. The present invention further relates to a process for carrying out a radical polymerization or copolymerization of unsaturated monomers, characterized in that the above described organic peroxide is used.
2. Description of the Related Art Statement
There are various factors, such as polymerization rate, polymerization degree and molecular weight distribution of the resulting polymer and the like, in the polymerization regulation. In the radical polymerization or copolymerization of unsaturated monomers, these factors have an intimate relation to the polymerization heat, and the flowability, workability and mechanical property of the resulting polymer. The regulation of polymerization is the most important problem in the field of polymer chemistry, particularly in the industrial field of polymer chemistry at present.
In general, the reciprocal of the number-average polymerization degree Pn of a polymer formed in the initial stage of a radical polymerization of unsaturated monomers, and the polymerization rate are represented, as described on pages 387-388 in "Shin Jikken Kagaku Koza, Vol. 19, Kobunshi Kagaku [I]" edited by the Chemical Societ of Japan and published by Maruzen (1975), by the following formulae (1) and (2): ##EQU1## (in the formulae (1) and (2), k.sub.trM, k.sub.trl and k.sub.trA represent the rate constants of chain transfer of polymer radical into the unsaturated monomer, polymerization initiator and polymerization regulator, respectively; k.sub.t and k.sub.p represent the rate constants of termination reaction and propagation, respectively; k.sub.d and f represent the decomposition rate constant of polymerization initiator and the initiator efficiency, respectively; [I], [M] and [A] represent the concentrations of polymerization initiator, unsaturated monomer and polymerization regulator, respectively; R.sub.p represents the polymerization rate; and X represents the ratio of disproportional termination reaction.)
In the formula (1), the first, second and third terms of the right side are terms based on the chain transfer reactions of the polymer radical to the unsaturated monomer, polymerization initiator and polymerization regulator, respectively; and the fourth term of the right side is a term based on the termination reaction between polymer radicals.
According to the formula (1), the polymerization degree decreases with the increase of the polymerization rate, and further decreases with increasing the concentration of the polymerization regulator. Accordingly, the polymerization degree of a polymer to be formed is generally regulated by changing the polymerization rate or by adding to the polymerization system a polymerization regulator having a known chain transfer constant represented by k.sub.trA /k.sub.p.
For example, the above described publication describes that the formula (1) is established in the polymerization of styrene initiated by azoisobutyronitrile and dibenzoyl peroxide. Japanese Patent Application Publication No. 10,046/59 discloses that the polymerization rate is increased with increasing the concentration of dibenzoyl peroxide, and polymers having various polymerization degrees can be obtained.
Japanese Patent Laid-open Application No. 52,886/73 discloses that, when alkyl mercaptan and carbon tetrabromide are used, the polymerization degree of the resulting polymer is decreased and the polymer solution has a very low relative viscosity.
Belgian Patent No. 660383 discloses that a peroxy carbonate represented by the following general formula (II) ##STR1## wherein R represents a tert-alkyl group or a tert-aralkyl group; and R' represents an alkyl group, an aralkyl group, an aryl group or an alkoxyalkyl group, can be utilized as a polymerization initiator for unsaturated monomer.
The polymerization-regulating technique which uses conventional polymerization initiator and polymerization regulator has several drawbacks, which are as follows.
That is, when the polymerization rate is higher, the control of the polymerization reaction becomes very difficult due to the increase of polymerization heat and to the rapid increase of viscosity in the polymerization system. For example, in the production of methyl methacrylate resin sheet, a syrup is used in order to suppress the heat generation due to polymerization or to prevent the shrinkage of the resulting polymer. In this case, the use of a syrup having a proper viscosity and having a high polymer content is desired. However, the use of an ordinary polymerization initiator causes difficulties in the control of polymerization reaction, and the resulting syrup has often an extraordinarily high viscosity.
In the recent production of styrene resin, the styrene resin is demanded to have excellent formability due to the development of a precise and high-speedy injection molding machine. However, it is generally difficult to produce a polymer having excellent formability due to the formation of a polymer having a very high molecular weight by the gel effect during the latter stage of the polymerization reaction. Further, when the polymerization initiator is used in a larger amount in order to lower the molecular weight of the resulting polymer, the resulting polymer has a poor mechanical property due to the formation of low molecular weight polymer. Therefore, it is a very important problem to produce a polymer having a uniform molecular weight.
In the above described method for producing a polymer by the use of carbon tetrabromide, the resulting polymer is poor in the thermal stability, and hence the polymer colors and decomposes noticeably at its processing temperature and is poor in the practical value of the formed article. Further, in the above described method for producing a polymer by the use of an alkyl mercaptan, it is known that the unpleasant odor of the alkyl mercaptan causes serious troubles in the use, and further unreacted alkyl mercaptan remaining in the resulting polymer affects adversely on the polymer. In the peroxy carbonate represented by the above described general formula (II), an isopropyl group, benzyl group, cycloalkyl group or the like is used as R'. However, the peroxy carbonate having such group is very poor in the polymerization-regulating ability.